This invention relates to improved processes for remineralizing subsurface lesions and mineralizing exposed dentinal tubules in teeth.
The primary component of the enamel and dentin in teeth is calcium phosphate in the form of calcium hydroxyapatite. This material is highly insoluble at normal oral pHs. However, carious lesions form in teeth when they are subjected to acids produced from the glycolysis of sugars by the action of various oral bacteria. This is because calcium phosphate salts are more soluble in acidic media.
Saliva is supersaturated with respect to calcium and phosphate ions. Saliva therefore helps protect teeth against demineralization and can slowly remineralize teeth which have become demineralized by acids. It is well known that the presence of fluoride ions can enhance the natural remineralization process and this is one of the accepted mechanisms by which fluoride toothpastes and rinses protect against caries. The efficacy of fluoride containing toothpastes and rinses to remineralize teeth is limited by the modest levels of calcium and phosphate in saliva. It is evident from the prior art that it is highly desirable to increase the available concentration of calcium and phosphate ions in the oral cavity to speed up the remineralization process. However, because of calcium phosphate's low solubility at the pH of saliva, the addition of higher levels of dissolved calcium and phosphate ions is not easily accomplished.
Remineralization of dental enamel has been carried out experimentally both in vivo and in vitro. Some studies have concentrated on the remineralizing properties of saliva and synthetic solutions supersaturated with respect to hydroxyapatite. Such studies comprise the subject matter of U.S. Pat. Nos. 3,679,360 (Rubin) and 4,097,935 (Jarcho).
Generally, the supersaturated solutions or slurries used in these patents for remineralization experiments have been prepared from a single form of calcium phosphate. When a carious lesion is flooded with one of these supersaturated solutions, the calcium and phosphate ions in the form of precipitated hydroxyapatite remineralize the lesion.
However, these solutions are impractical for use for several reasons. First, the amount of calcium and phosphate ions available for remineralization in these supersaturated solutions is too low. It is reported that it takes approximately 10,000 unit volumes of the usual supersaturated solution to produce one unit volume of mineral. Thus, remineralization by this method requires both an excessive volume of fluid and an excessive number of applications. The supersaturated solutions are inherently limited in this respect because they cannot maintain their supersaturated state. When the hydroxyapatite precipitates out to the point where the solution is no longer supersaturated, new supersaturated solution must be introduced or the remineralization process stops.
Another problem with single calcium phosphate slurries is that as the hydroxyapatite precipitates out of solution, the pH of the solution changes. Unless the old solution is removed from contact with the tooth material, the solution may become too acidic or alkaline and damage the dental tissue.
Another problem with known remineralization techniques is that the remineralization may stop before the lesion is completely remineralized due to build up of the remineralized tooth material in or on the outer layer of the tooth's surface. This build up occurs when the rate of remineralization is too fast and prevents the diffusion of the mineral into the deeper regions of the lesion, thus thwarting the full remineralization of the tooth.
There is also a need for a method of remineralizing dental enamel that does not require excessive amounts of solution and inordinately long or frequent exposure times.
U.S. Pat. No. 4,080,440 (Digiulio et al) discloses a metastable solution of calcium and phosphate ions at a low pH (between 2.5 and 4.0) under which conditions the solubility of calcium phosphate salts is high. After penetration of the solution into demineralized enamel, remineralization results from the precipitation of calcium phosphate salts when the pH rises. Fluoride ions can be included in the metastable solution. A significant disadvantage of the use of metastable solutions is that the relatively low pH might demineralize the dental enamel and/or injure other tissue.
U.S. Pat. Nos. 4,177,258, 4,183,915 and 4,348,381 (Gaffar et al) provide for a remineralizing solution containing supersaturated concentrations of calcium ions, phosphate ions and a fluoride source stabilized by the presence of an antinucleating agent such as diamine tetramethylenephosphonic acid, ethylenediamine tetramethylenephosphonic acid, 2-phosphonobutane-tricarboxylic acid-1,2,4, or the water-soluble salts thereof. This solution is preferably adjusted to the neutral pH range where it is alleged to most effectively remineralize subsurface lesions. Even though the antinucleating agent would be expected to stabilize the solution, equilibrium of the supersaturated concentrations is still found difficult to maintain and avoid precipitation of hydroxyapatite and changes in the pH of the solution.
U.S. Pat. Nos. 4,083,955 (Grabenstetter et al) and 4,397,837 (Raaf et al) provide a process for remineralizing demineralized enamel by the consecutive treatment of tooth surfaces with separate solutions containing calcium ions and phosphate ions. In this process, fluoride ions may be present in the phosphate solution. It is immaterial which ionic solution is used to treat the teeth first. By sequentially applying calcium and phosphate ions to the tooth surface, high concentrations of the ions are able to penetrate into lesions in solution form, where they precipitate as a calcium phosphate salt when ions from the second treatment solution diffuse in. While apparently successful, this method involves the inconvenience of a plurality of sequential applications which can also be found to be time-consuming.
U.S. Pat. No. 4,606,912 (Rudy et al) provides a method of making a clear aqueous mouthwash solution capable of remineralizing lesions in teeth by forming an aqueous solution containing a source of calcium ions and a chelating agent for calcium ions, causing the chelation of at least 50% of the calcium ions and subsequently adding a source of phosphate ions to the aqueous solution. Here too, while somewhat effective, the addition and necessary control of the amount of chelating agent makes the concept impractical.
U.S. Pat. No. 5,427,768 to Tung discloses carbonated calcium phosphate solutions which are used to deposit calcium phosphate compounds on and in the teeth. According to Tung, the invention therein takes advantage of the fact that at alkaline pH, aqueous solutions are capable of maintaining a greater amount of phosphate ions and carbonate ions in solution under atmospheric conditions. These alkaline solutions can then be mixed with acidic calcium solutions to create carbonated solutions useful for treating dental tissue. When the two solutions are mixed, the mixed solution is supersaturated with respect to calcium phosphate and carbon dioxide under atmospheric pressure. As the carbon dioxide evaporates, the pH of the solution increases, and calcium phosphate precipitates out of solution.
The Tung patent discussed above requires the use of carbonate compounds in the remineralization method taught therein. It would be desirable to provide a remineralization method which does not require or use a carbonate compound.
A primary object of the present invention is to provide a process for remineralizing subsurface lesions in teeth and for mineralizing exposed dentinal tubules, wherein the process is capable of effectively incorporating calcium ions, phosphate ions, and, if desired, fluoride ions into the dental enamel.
Another object of the present invention is to provide a process which effectively remineralizes subsurface lesions and/or mineralizes exposed dentinal tubules in teeth, wherein the process does not use carbonate compounds.
These and other objects which are achieved according to the present invention can be discerned from the following description.